Conventionally, when a vehicle's direction is changed, as when turning along a curve, a differential apparatus provides a differential for right and left wheels to secure a smooth performance. However, if one of the wheels slips on a road surface having a small coefficient of friction, such as a road in a swamp, the drive force cannot be structurally transmitted to the other wheel, and thus the vehicle cannot be moved out of the swamp. To solve this problem, the differential apparatus has a differential restricting mechanism for restricting the differential, which serves to move the vehicle out of the swamp when one of the wheels slips on a swampland road, the differential being generated between the right and left wheels.
The differential apparatus provided with such a differential restricting mechanism is disclosed in Japanese published patent 57-4536, for example, and is shown in FIG. 1.
In FIG. 1, a differential carrier 101 has a differential gear mechanism 102 therein, and rotatably supports a differential casing 104 of the differential gear mechanism 102 through a bearing 103. A cylindrical portion 105 is formed in the differential carrier 101. When an operating oil is supplied to the cylindrical portion 105, a piston 106 disposed within the cylindrical portion 105 presses, through a pressing member 107, frictional plates 108 disposed in the differential casing 104 as a differential control means. When the frictional plates 108 are pressed by the piston 106, the differential casing 104 and a side gear 109 of the differential gear mechanism 102 are integrally rotated, thereby restricting the differential between the right and left wheels.
However, in such a conventional differential apparatus having the differential restricting means 108, when the operating oil is supplied to the cylindrical portion 105, the piston 106 presses the frictional plates 108 through the pressing member 107 by the pressure of the operating oil. At this time, the differential casing 104 is pressed to the right in FIG. 1 together with the frictional plates 108. When the differential casing 104 is pressed in a rightward direction, the bearing 103 disposed between the differential casing 104 and the differential carrier 101 is also pressed to the right, so that an inner race 103a of the bearing 103 is pressed to the right. When the inner race 103a is pressed to the right, a roller 103b of the bearing 103 is rotated while being vibrated, thereby reducing the durability of the bearing 103.
Further, the conventional power transmission apparatus is large-sized, so the mechanical strength is low, and the design of the apparatus must be greatly changed to increase the rigidity. Moreover, vibrations tend to be generated in the apparatus.